Epidermoid and dermoid tumors, also referred to as epidermoid or dermoid cysts are slow growing benign lesions that result form an error of cell migration during embryonic development. These lesions develop when cells in the developing embryo that were destined for the skin, hair or nail tissue become entrapped in the developing brain or spinal cord. These trapped cells ultimately produce what is called an inclusion cyst and the cyst contents can vary depending on the exact cell type that was trapped. The distinction between epidermoid and dermoid cysts is that epidermoid cysts do not contain hair or sebaceous glands. Rarely these cysts can spontaneously release their contents into the brain or cerebrospinal fluid causing a form of chemical meningitis.
Epidermoid cysts are benign masses, frequently located off to the side of the brain or skull such as the cerebellopontine angle (an area along the side of the brainstem), near the pituitary gland, or within the skull. Dermoid cysts tend to me more midline in location but are relatively rare in the brain and instead occur more frequently in the spine, face or scalp. These tumors also are referred to as germ cell tumors because the original skin layer within the embryo that these trapped cells originated from is known as a germ layer.
Intracranial Epidermoid and dermoid tumors are usually slow growing and, therefore, may grow to a large size before causing symptoms. The symptoms of an intracranial epidermoid and dermoid are caused by the pressure the growing tumor exerts on surrounding brain and can vary depending on location. These tumors can occur in a variety of places and therefore cause a wide range of symptoms, although they tend to occur in specific regions around the brain. Depending on the location of the mass, epidermoid and dermoid tumors may cause headaches, nausea, seizures, vision loss, facial pain, weakness or numbness in the limbs or face, and gradual changes in mood or personality. The symptoms tend to increase in severity as the tumor grows in size. If the cyst ruptures and spill its contents, it can cause repeated bouts of severe meningitis, with symptoms including fever, headache, and neck stiffness.
These tumors are diagnosed with a neurological examination followed by imaging studies of the brain, usually a computed tomography (CT) or magnetic resonance imaging (MRI) scan. The scan is often performed with a contrast dye to make the border and details of the tumor more visible in relation to the surrounding normal brain. However, these tumors are often indistinct from the surrounding brain and a specialized MRI sequence (diffusion imaging) has to be performed in order truly visualize the tumor. The MRI scan provides detail information regarding the exact size, location and other structures involved by the tumor. Only examination of a patient’s tumor tissue under a microscope can confirm an exact diagnosis. This tissue is usually obtained with a biopsy or tumor resection.
The primary treatment for symptomatic dermoid or epidermoid cysts is surgical removal. In general the goals of surgical removal are to remove the cyst contents but to also remove the cyst lining if safely possible. Chemotherapy and radiation generally do not play a significant role in the treatment of these lesions. Depending on the location of the tumor, surgical removal can include minimally invasive techniques including endoscopic transnasal approaches or open skull base approaches. In general, surgery for these tumors is performed with an intraoperative neuro-navigation system that localizes the excat position of the lesion and depending on the location of the tumor, neuro-monitoring, especially of the cranial nerves is performed.